JP2769773B2 - Suspension polymerization stabilizer and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydroxyapatite-based suspension polymerization stabilizer used for producing a vinyl polymer by a suspension polymerization method, and a method for producing the same.

[0002]

2. Description of the Related Art As a method for producing a spherical polymer,
The suspension polymerization method is known. In this suspension polymerization method, since the obtained polymer is in the form of beads or pearls,
Also known as "bead polymerization" or "pearl polymerization", it is easy to remove heat in large equipment and not only can obtain high-performance polymer, but also suitable for multi-product production,
Particularly, it is useful for suspension polymerization of styrene or a vinyl monomer copolymerizable therewith.

In general, suspension polymerization is carried out by dispersing monomer, dispersant or suspension stabilizer and polymerization initiator with monomer particles under vigorous stirring in the presence of a monomer-insoluble dispersion medium such as water. Thus, the performance of the dispersant or stabilizer strongly influences the polymerization operation as well as the quality of the resulting polymer, as the polymerization proceeds within the dispersed individual monomer particles and forms the polymer in that form.

Heretofore, as a stabilizer for suspension polymerization, there have been known water-soluble polymer-based stabilizers such as polyvinyl alcohol and CMC, and inorganic fine particles represented by basic phosphates, particularly hydroxyapatite. Each is used properly according to the purpose. Among them, the hydroxyapatite suspension polymerization agent is disclosed in detail in, for example, JP-B-29-1298 and JP-B-60-6490. In using these stabilizers, in order to enhance reproducibility and reliability as a stabilizer, a method of heat-treating with a surfactant (Japanese Patent Publication No. 47-23666) is used. (Japanese Patent Publication No. 48-42220), a method of sonication (Japanese Patent Publication No. 47-38631) or a method using an apatite slurry having a sedimentation half-life of at least 15 minutes (Japanese Patent Publication No. 54-42231). No. 44313) has been proposed.

However, even with hydroxyapatite, which is said to have a high suspension stabilizing ability, the monomer particles act as individual reaction systems, in which individual polymerization proceeds while forming radicals therein. In order to obtain uniform polymer particles in the polymerization reactor, the performance of the stabilizer has an essential and subtle effect. That is, depending on the quality of the apatite, the polymer beads are united to form a coagulum or rice cake-like form, or adhere as a scale to the wall surface inside the apparatus, causing operation trouble. In order to prevent such a phenomenon, measures such as increasing the amount of the stabilizer used have been taken, but this not only increases the cost but also deteriorates the quality of the polymer. For this reason, development of a higher-performance stabilizer for suspension polymerization has been demanded.

[0006] In this regard, the above-mentioned Japanese Patent Publication No. 54-44313.
The stabilizer for suspension polymerization described in Japanese Patent Application Publication No. H07-27138 focuses on the fact that the sedimentation characteristics of the hydroxyapatite slurry gives a high correlation to the suspension polymerization result, and the slurry obtained directly during the production of apatite is used as the stabilizer. In addition, there is an advantage that agglomeration phenomenon of particles generated when the slurry is dried and powdered can be avoided. However, even the apatite slurry produced by such a reaction has insufficient reliability,
Frequently, adhesion and agglomeration between particles during the polymerization reaction and growth of the particles over time are inevitable.

[0007]

Generally, particles in a slurry obtained from a process for producing apatite alone are 0.5% or less.
Although it has a very fine particle size of less than μm, it easily agglomerates due to surface energy to form a particulate behavior, which results in a non-uniform particle size of the polymer.
Therefore, if a stabilizer having properties capable of always forming uniform polymer particles during suspension polymerization can be ensured, it is possible to improve the polymer quality.

The present inventors have conducted various studies on the relationship between particle properties and agglomeration when a slurry obtained directly from the production of apatite is used as a stabilizer for suspension polymerization, and found that CaO / P _When the properties of the hydroxyapatite particles contained in the slurry having a specific value of ₂ O ₅ or more have a specific fineness and particle size distribution, agglomeration is effectively suppressed, and the uniformity of the polymer particles is significantly improved. Clarified that.

The present invention has been developed on the basis of the above-mentioned findings, and its object is to provide a non-agglomerated hydroxyapatite suspension polymerization capable of always producing polymer particles having a uniform and sharp particle size distribution. And a method for producing the same.

[0010]

The stabilizer for suspension polymerization according to the present invention for achieving the above object is CaO / P ₂ O.
_{5 is} a hydroxyapatite slurry having a weight ratio of at least 1.30, wherein the average particle diameter of the dispersed hydroxyapatite particles is 1 μm or less, 70% of the particle content is 0.65 μm or less, and 4 μm or more. It is characterized by having a particle size distribution not exceeding 5%.

In the above structure, the average particle size and the particle size distribution of the apatite particles are values measured by a particle size distribution measuring method using a coaltan counter.

In the present invention, the slurry composition of hydroxyapatite (hereinafter referred to as “apatite”) is Ca
A weight ratio of O / P ₂ O ₅ of at least 1.30 is a prerequisite for preparing a stable apatite slurry. In addition, when the average particle diameter of the apatite particles dispersed in the slurry is 1 μm or less, 70% of the particle content is 0.65 μm or less, and 4 μm or more satisfies the particle size distribution not exceeding 5%. A slurry of a dispersion system that does not cause secondary aggregation is obtained. Therefore, even when the weight ratio of CaO / P ₂ O ₅ is 1.30 or more, for example, aggregation or sedimentation occurs in the particle properties in which the average particle diameter exceeds 1 μm and the particles of 4 μm or more exceed 5%. As a result, the function of uniformizing the granular properties of the polymer during suspension polymerization is not exhibited.

The production method according to the present invention for obtaining a suspension polymerization stabilizer having the above-mentioned particle properties is characterized in that apatite is used at a weight ratio of phosphoric acid to milk of lime of CaO / P ₂ O ₅ of at least 1.30. It is a constitutive requirement that the resulting slurry is then subjected to a strong shear dispersion treatment.

Apatite is produced by a method in which phosphoric acid and milk of lime are gradually reacted. At this time, the weight ratio of CaO / P ₂ O ₅ is adjusted to at least 1.30 to produce a stable apatite slurry. . The slurry concentration was 8
It is preferred that the content be in the range of 20 to 20% by weight.

Next, the apatite slurry is subjected to a strong shearing dispersion treatment to form a homogeneously dispersed phase. As the apparatus used in this treatment step, a mechanism capable of exerting a strong shearing force on the slurry is used. As an industrially suitable apparatus, a homogenizer commonly used in the paint, ink or pigment manufacturing industries is used. , A colloid mill, a cooling blender, and the like. In addition, an ultrahigh-pressure emulsifying and dispersing apparatus of a type in which particle agglomeration is broken by colliding a high-pressure water stream is also preferably used for the purpose of the present invention. In the strong shear dispersion treatment, the apatite particles present in the dispersion after the treatment have an average particle diameter of 1 μm or less, and 70% of the particle content is 0.65 μm or less, and 4 μm
The conditions are set so that the particle properties do not exceed 5%.

Hydroxyapatite is produced as submicron particles during the synthesis reaction, but after the reaction, due to its cohesive energy, the particles are aggregated until the system becomes stable and become 1 μm or more. However, when the strong shear dispersion treatment of the present invention that breaks agglomeration is performed at this time, the aggregating force is weakened, and not only a preferable particle size distribution is recovered, but also the above-mentioned particle properties can be easily stably maintained. Becomes

The apatite slurry produced by the above process is used as a polymerization stabilizer without changing the conventional suspension polymerization operation. Examples of the monomer to be subjected to suspension polymerization include, for example, substituted or unsubstituted styrene,
One or two selected from (meth) acrylates, acrylonitrile, vinyl esters, and olefins
At least one kind of monomer capable of suspension polymerization can be used. The amount of the stabilizer for suspension polymerization varies depending on its physical properties and conditions of suspension polymerization, but in most cases, 0.1 to 1.0% by weight of apatite (in terms of solid content), preferably 0.1% by weight, of the monomer. A highly reliable effect can be expected within a small range of 15 to 0.8% by weight. When using the stabilizer for suspension polymerization of the present invention, if necessary, other stabilizers, for example, water-soluble polymer compounds such as polyvinyl alcohol, CMC, and gelatin, and surfactants such as sodium dodecylbenzenesulfonate. An agent, a pH adjuster, a specific gravity adjuster or a viscosity adjuster may be appropriately used in combination.

[0018]

The stabilizer for suspension polymerization according to the present invention is CaO / P
Apatite slurry having a weight ratio of ₂ O ₅ of at least 1.30, wherein the average particle diameter of dispersed apatite particles is 1 μm or less, and 70% of the particle content is 0.65 μm or less, and 4% or more is 5%. Because of its particle size distribution not exceeding, its unique fine particle size functions to suppress the occurrence of sedimentation and aggregation phenomena and to form a uniform and sharp particle size distribution of the produced polymer during suspension polymerization. .

Further, according to the production method of the present invention, excellent dispersibility can be obtained through a simple operation of directly subjecting a slurry obtained from an apatite production process to a strong shear dispersion treatment,
A high-performance stabilizer for suspension polymerization without secondary aggregation can be industrially advantageously produced.

[0020]

【Example】

Examples 1 to 5, Comparative Example 1 Phosphoric acid was added to lime milk from which slaked lime had been sufficiently deagglomerated while controlling the electric conductivity while monitoring the electric conductivity. The amount of phosphoric acid added is CaO / P ₂ O ₅
Is set to be 1.35 to 1.40,
An apatite slurry having a solid content of 10% by weight was prepared. The obtained slurry was subjected to a strong shear dispersion treatment under a predetermined condition using a strong shear disperser (“TK homomixer M type” manufactured by Tokushu Kika Kogyo Co., Ltd.).

Example 6 The same apatite slurry as in Example 1 was used in an ultrahigh-pressure emulsifying and dispersing machine [T.K Nanomizer L, manufactured by Tokushu Kika Kogyo Co., Ltd.]
A-31 type "] and a strong shear dispersion treatment at a treatment pressure of 1200 kg / cm ² .

[Evaluation of Particle Properties and Dispersion Characteristics]
Table 1 shows the particle properties and dispersion characteristics of each apatite slurry subjected to the strong shear dispersion treatment according to Comparative Example 6 and Comparative Example 1 in comparison with the conditions of the strong shear dispersion treatment. The evaluation of dispersibility was based on the sedimentation half-life of the dispersion after the strong shear dispersion treatment by the following measurement method. For comparison, the dispersion characteristics of an apatite slurry (Comparative Example 1) not subjected to a strong shear dispersion treatment were similarly evaluated, and the results are shown in Table 1.

Particle properties: sodium tripolyphosphate
Water is added to 3 g to make 300 ml. Then, the sample (10wt
% Slurry) and disperse for 3 minutes with a mixer. This is measured with a Coulter counter particle size distribution analyzer (TA-
Measured with an 11-inch aperture diameter of 20 μm). In Table 1, V50
Is the average particle size (μm). Dispersibility (sedimentation half-life): 100 ml of a slurry obtained by diluting a sample to a solid concentration of 0.15 g / 100 ml is placed in a sedimentation tube, stoppered, vigorously shaken for 1 minute, and allowed to stand. In this state, the sedimentation volume at normal temperature (25 ° C.) or the time (minute) for the supernatant to reach half of 50 ml is defined as the sedimentation half-life (t1 / 2).
Define and ask.

[0024]

[Table 1]

From the results in Table 1, all the apatite slurries according to the examples manufactured according to the present invention show excellent dispersibility. In Japanese Patent Publication No. 54-44313,
It has been shown that the suspension stability in suspension polymerization correlates with the sedimentation characteristics of the apatite slurry with a highly reliable contribution, but the apatite slurry according to the present invention has a sedimentation half-life (t1 / 2) is 30 minutes or more, and the performance as a stabilizer for suspension polymerization is sufficiently guaranteed.

Next, using the apatite slurries of Examples 2, 5, 6 and Comparative Example 1 as a stabilizer for suspension polymerization, a styrene monomer polymerization reaction was carried out under the following operating conditions. In a reaction vessel equipped with a 500 ml three-neck separable flask and a 6-blade disk turbine impeller, 150 g of styrene monomer, 0.01 g of sodium dodecylbenzenesulfonate, 4.8 g of benzoyl peroxide, 3.5 g
Stabilizer (apatite slurry 10%) and water 350
g at 70 ° C. while stirring at a stirring speed of 200 rpm.
The suspension polymerization was carried out at a temperature of. Then, the polymer was recovered by centrifugation in a conventional manner, and the apatite was dissolved with hydrochloric acid, washed with water and dried to produce a styrene polymer. The average particle size and uniformity of the obtained polymer particles were measured, and the results are shown in Table 2.

The particle size distribution of the polymer particles was measured by a sieve classification method. The uniformity of the particle size was evaluated by defining a value calculated by the following equation as a uniformity coefficient. U _T = U _90/40 + U _{60/10 In the} above equation, U _90/40 is a value obtained by dividing a 90% diameter by a 40% diameter, and U _60/10 is a value obtained by dividing a 60% diameter by a 10% diameter. is there.
Therefore, the closer the uniformity coefficient is to 2, the better the uniformity of the particle size.

[0028]

[Table 2]

From the results in Table 2, it can be seen that the styrene polymer produced using the stabilizer for suspension polymerization satisfying the requirements of the present invention is:
The beads were found to be excellent in uniformity.

[0030]

As described above, according to the present invention, it is possible to produce a polymer having a uniform and sharp particle size distribution at the time of polymerization without any sedimentation or aggregation by directly using a slurry obtained from a hydroxyapatite manufacturing process. And a high-performance apatite-based suspension polymerization stabilizer that can be used. In particular, the stabilizer for suspension polymerization of the present invention is extremely useful for the purpose of homopolymerizing or copolymerizing (for example, ABS) substituted or unsubstituted styrene.

────────────────────────────────────────────────── (5) References JP-A-5-222103 (JP, A) JP-A-53-90386 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08F 2/18 C01B 25/32

Claims (2)

(57) [Claims] 1. A slurry of hydroxyapatite having a weight ratio of CaO / P ₂ O ₅ of at least 1.30, wherein the dispersed hydroapatite particles have an average particle size of 1
μm or less, 70% of the particle content is 0.65 μm or less,
A stabilizer for suspension polymerization, wherein the particle size distribution of 4 μm or more does not exceed 5%. 2. The weight ratio of phosphoric acid to milk of lime caO / P ₂ O
_{5. A} method for producing a stabilizer for suspension polymerization, which comprises producing hydroxyapatite in a ratio of at least 1.30, and subjecting the resulting slurry to a high shear dispersion treatment.